3,407 research outputs found
Effects of X-ray irradiation on human spermatogenesis
Direct cell kill and inhibition of mitosis have been suggested as mechanisms to explain the occurrence of absolute sterility following the irradiation of the testes. In order to obtain information on the existence and dose dependency of the mechanisms for man, a controlled study was initiated. Sixty-four men received a single midorgan dose to both of their testes ranging from 7.5 to 400r (f = .95). It was deduced from resulting pre-sterile period and sterile period data that both cell kill and mitosis halting mechanisms were operating. The maximum observed sterile period was 501 days with eventual recovery observed in each individual where the follow-up was complete. Thus man appears to be highly radiosensitive in regard to temporary sterility but quite radioresistant in regard to permanent sterility
Minimal and Maximal Operator Spaces and Operator Systems in Entanglement Theory
We examine k-minimal and k-maximal operator spaces and operator systems, and
investigate their relationships with the separability problem in quantum
information theory. We show that the matrix norms that define the k-minimal
operator spaces are equal to a family of norms that have been studied
independently as a tool for detecting k-positive linear maps and bound
entanglement. Similarly, we investigate the k-super minimal and k-super maximal
operator systems that were recently introduced and show that their cones of
positive elements are exactly the cones of k-block positive operators and
(unnormalized) states with Schmidt number no greater than k, respectively. We
characterize a class of norms on the k-super minimal operator systems and show
that the completely bounded versions of these norms provide a criterion for
testing the Schmidt number of a quantum state that generalizes the
recently-developed separability criterion based on trace-contractive maps.Comment: 17 pages, to appear in JF
An automated and versatile ultra-low temperature SQUID magnetometer
We present the design and construction of a SQUID-based magnetometer for
operation down to temperatures T = 10 mK, while retaining the compatibility
with the sample holders typically used in commercial SQUID magnetometers. The
system is based on a dc-SQUID coupled to a second-order gradiometer. The sample
is placed inside the plastic mixing chamber of a dilution refrigerator and is
thermalized directly by the 3He flow. The movement though the pickup coils is
obtained by lifting the whole dilution refrigerator insert. A home-developed
software provides full automation and an easy user interface.Comment: RevTex, 10 pages, 10 eps figures. High-resolution figures available
upon reques
The effects of nuclear spins on the quantum relaxation of the magnetization for the molecular nanomagnet Fe_8
The strong influence of nuclear spins on resonant quantum tunneling in the
molecular cluster Fe_8 is demonstrated for the first time by comparing the
relaxation rate of the standard Fe_8 sample with two isotopic modified samples:
(i) 56_Fe is replaced by 57_Fe, and (ii) a fraction of 1_H is replaced by 2_H.
By using a recently developed "hole digging" method, we measured an intrinsic
broadening which is driven by the hyperfine fields. Our measurements are in
good agreement with numerical hyperfine calculations. For T > 1.5 K, the
influence of nuclear spins on the relaxation rate is less important, suggesting
that spin-phonon coupling dominates the relaxation rate at higher temperature.Comment: 4 pages, 5 figure
Answer to the comment of Chudnovsky: On the square-root time relaxation in molecular nanomagnets
Answer to the comment of E. Chudnovsky concerning the following papers:
(1) N.V. Prokof'ev, P.C.E. Stamp, Phys. Rev. Lett.80, 5794 (1998).
(2) W. Wernsdorfer, T. Ohm, C. Sangregorio, R. Sessoli, D. Mailly, C.
Paulsen, Phys. Rev. Lett. 82, 3903 (1999).Comment: 1 page
The Roll Away Saloon
With his animated tales of Zane Grey, Butch Cassidy, and the Robbers Roost gang, Rider creates an engaging and believable picture of the joys and hardships of cowboy life
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